The present invention relates to a dusting-inhibited cement composition, which is treated to inhibit the emission of cement dust during transportation or storage of the cement.
For the purpose of preventing various bad effects caused by cement dust emitted into the air from cement during transportation or storage, there have been developed dusting-inhibited cements which are inhibited from the dust emission into the air by catching the cement powder with random nets of sub-micron size fine polytetrafluoroethylene (hereinafter polytetrafluoroethylene is denoted as PTFE) fibril obtained by adding fibrillatable PTFE to cement and subjecting the mixture to compression-shear to fibrillate the PTFE
As to the art for manufacturing such dusting-inhibited cement, mention is made in Japanese Kokoku Patent Publication Hei 5-24872.
Further, Japanese Kokoku Patent Publication Sho 52-32877 discloses that a mixture of fibrillatable PTFE and a powdery material is subjected to compression-shear at 20xcx9c200xc2x0 C. to fibrillate the PTFE so as to inhibit emission of dust from the powdery material.
Bulk density of cement subjected to the dusting-inhibiting process based on the art disclosed in Japanese Kokoku Patent Publication Hei 5-24872 or Sho 52-32877 tends to be lowered with entrained air in the powder due to the existence of the PTFE fibrils. Furthermore, strength of the concrete or mortar using the dusting-inhibited cement decreases to about 85xcx9c95% when compared to those without the treatment. Thus, an improvement in the strength has been desired.
The present inventors made studies on the cause of the decrease in strength of the concrete or mortar using the dusting-inhibited cement, and found out that numerous air bubbles formed in the concrete or mortar by the influence of the PTFE dusting-inhibiting agent brought about the decrease in compressive strength of the concrete or mortar made from the dusting-inhibited cement.
The problem to be solved by this invention is to provide a dusting-inhibited cement composition, which hardly emits dust and further capable of improving strength of concrete or mortar obtained therefrom.
A dusting-inhibited cement composition according to the present invention comprises 100 weight parts of cement, 0.01xcx9c0.1 weight parts of fibrillatable polytetrafluoroethylene and 0.001xcx9c1.0 weight parts of alcohol base antifoamer and/or silicone base antifoamer.
The fibrillatable PTFE is desirable to be fibrillated wholly or mostly for raising the dusting-inhibiting effect. The fibrils are formed when the fibrillatable PTFE is mixed with cement etc., and the mixture is subjected to the compression-shear for preparing the dusting-inhibited cement composition of the invention.